The disclosure of Japanese Patent Application No. 11 319824 filed on Nov. 10, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a vehicular brake apparatus for braking a vehicle and to a control method for the apparatus. More particularly, the invention relates to a vehicular brake apparatus capable of detecting a variation in wall thickness of a disc brake and eliminating or suppressing the wall thickness variation, and to a control method for the apparatus.
2. Description of Related Art
A vehicular brake apparatus described in Japanese Laid-Open Application No. 4-278872 brakes the vehicle by braking rotations of wheels. To brake rotation of the wheels, brake pads (friction members) are pressed against brake discs connected to the wheels so as to cause friction forces between the brake discs and the brake pads.
However, it is difficult to set the rotating axis of a wheel perfectly perpendicular to a brake disc. Therefore, it is often the case that a brake disc slightly wobbles while rotating. If brake pads are pressed against a brake disc turning in a wobbling state, there occurs a slight wall thickness variation in a circumferential direction of the brake disc. Occurrence of such a variation in wall thickness may become a cause of vibrations of the wheel during braking, or may cause the reaction force exerted on the brake pedal to finely fluctuate, and may give a disagreeable feel to a driver of the vehicle.
If the wall thickness variation of a brake disc is great, a portion of the brake disc may contact a brake pad even when brake operation is not performed, that is, generally termed brake dragging may occur. If such brake dragging occurs, a problem of an accelerated wear of the brake pads is likely to occur.
Accordingly, it is one object of the invention to provide a vehicular brake apparatus and control method capable of detecting a variation in the wall thickness of a brake disc and capable of eliminating the wall thickness variation.
In accordance with one aspect of the invention, a vehicular brake apparatus having a disc brake mechanism that brakes rotation of a wheel by pressing a friction member against a brake disc, includes a wall thickness detector and a controller. The wall thickness detector detects a state of wall thickness, of the brake disc. The controller controls a state of contact between the brake disc and the friction member. Based on the state of wall thickness of the brake disc detected by the wall thickness detector, the controller controls the state of contact between the brake disc and the friction member in such a fashion that the friction member contacts a relatively great wall thickness portion of the brake disc more strongly than a relatively small wall thickness portion of the brake disc.
The vehicular brake apparatus of this aspect of the invention detects a state of wall thickness of the disc brake (a state of wall thickness variation) by using the wall thickness detector. Based on a result of the detection, the apparatus actively performs a control such that the friction member contacts a portion of the brake disc having a relatively great wall thickness more strongly than a portion of the brake disc having a relatively small wall thickness (including a control such that the friction member is kept from contacting the relatively small wall thickness portion). In this manner, the apparatus is able to decrease, the thickness of the relatively great wall thickness portion of the brake disc and thereby eliminate the wall thickness variation of the disc. The apparatus is also able to suppress generation of a variation in the wall thickness of the brake disc. Therefore, the apparatus is able to prevent problems attributed to a variation in the wall thickness of the brake disc, for example, vibrations during braking, and the like.
The state of contact between the brake disc and the friction member may be controlled while a vehicle is not under braking. Therefore, since the control for eliminating (suppressing) a variation in the wall thickness of the brake disc is performed while the vehicle is not under braking, the state of contact between the brake disc and the friction member can be set to an optimal state for eliminating (suppressing) the wall thickness variation of the brake disc. Hence, the wall thickness variation of the brake disc can be more effectively eliminated (suppressed).
The controller may cause the friction member to contact a portion of the brake disc having a relatively great wall thickness, while preventing the friction member from contacting a portion of the brake disc having a relatively small wall thickness. Therefore, since the friction member is not caused to contact a relatively small wall thickness portion of the brake disc, it becomes possible to reduce the wear of the friction member, in addition to the advantage of decreasing a thickness of the relatively great wall thickness portion of the brake disc. This can eliminate a variation in the wall thickness of the disc brake.
The controller may also variably control a force of the friction member pressing the brake disc in correspondence to a wall thickness variation of the brake disc. Therefore, since the state of contact between the brake disc and the friction member is variably controlled in correspondence to the state of wall thickness of the brake disc, it becomes possible to more quickly eliminate any wall thickness variation of the brake disc and more effectively make the wall thickness of the brake disc uniform.
The vehicular brake apparatus may further have the following construction. That is, the disc brake mechanism may be a hydraulic brake mechanism that presses the friction member against the brake disc by raising a brake liquid pressure in a wheel cylinder. The wall thickness detector may detect the state of wall thickness of the brake disc from a variation in the brake liquid pressure during braking of a vehicle. The controller controls the state of contact between the brake disc and the friction member by adjusting the brake liquid pressure. This construction makes it possible to perform the detection of the state of wall thickness of the brake disc by the wall thickness state detector and the control of the state of contact between the brake disc and the friction member by the controller, through the use of the brake liquid pressure. Therefore, by controlling the brake liquid pressure, a variation in the wall thickness of the brake disc can be eliminated (suppressed).
A vehicular brake apparatus in accordance with another aspect of the invention includes a disc brake mechanism, a fluctuation detector that detects a brake fluctuation, and a wall thickness state detector that detects a state of wall thickness of the brake disc based on the brake fluctuation. As a brake fluctuation, it is possible to detect a fluctuation in brake pressure in a wheel cylinder or a fluctuation in the torque of an electric motor that occurs together with rotation of a wheel.
In this vehicular brake apparatus, the state of wall thickness of the disc brake is detected based on, for example, a brake pressure fluctuation per rotation of the disc brake. Therefore, the apparatus is able to detect a wall thickness of the disc brake corresponding to the rotational position (angle) of the disc brake.
Still another aspect of the invention provides a control method for a vehicular brake apparatus having a disc brake mechanism that brakes rotation of a wheel by pressing a friction member against a brake disc. In the method, a state of wall thickness of the brake disc is detected. Based on the detected state of wall thickness of the brake disc, a state of contact between the brake disc and the friction member is controlled in such a fashion that the friction member contacts a relatively great wall thickness portion of the brake disc more strongly than it contacts a relatively small wall thickness portion of the brake disc.